Figure legends
Fig. 1. Bioreactor system and mixing impellers used in this study.
(A) Structure of a bioreactor. A water-jacketed 2.5-L glass vessel containing 2 L of medium. Air containing 5% CO2 was supplied at 50 mL/min onto the surface of medium; supply of pure O2 through sparger to the inside of medium was controlled by DO sensor to maintain > 2.8 mg O2/L. (B) Six flat turbine impeller (6FT). (C) Conventional elephant ear impeller (EE). (D) Double elliptical plates for reciprocal mixing (RM).
Fig. 2. Growth curves and viabilities of CHO-S cells.
(A) Cell viabilities. (B) Growth curves. CHO-S cells were cultivated in bioreactors with 6FT (grey triangle ▲), EE (open rectangle □), or RM (closed circle ●). Batch culture was started by seeding precultured cells in the bioreactor at 105 cells/mL. No significant difference in terms of cell number and cell viability was observed before 120 h. However, cell viability in 6FT and EE bioreactors rapidly decreased at around late stationary phase (120 h).
Fig. 3. Analyses of culture media for culturing CHO-S cells.
(A) Glucose concentration in media. (B) Lactate concentration in media. (C) Leaked LDH activity. CHO-S cells were cultivated in bioreactors with 6FT (grey triangle ▲), EE (open rectangle □), or RM (closed circle ●). No significant difference was observed before 80 h. After entering the early stationary phase (at approximately 80 h), lactate consumption became much more than lactate production. Concentration of lactate in bioreactor with RM decreased rapidly. Leaked LDH activity in bioreactors with 6FT and EE was drastically increased after late stationary phase (approximately 160 h) while that in reciprocal bioreactor was suppressed to lower level.
Fig. 4. Computational fluid dynamics analyses at Pv = 36 W/m3.
(A–D) Velocity vectors. (E–H) Contours of shear stress. (A, E) Rotary mixing with EE. (B–D, F–H) Reciprocal mixing with RM.
Fig. 5. Distribution of shear stress in the bioreactors.
Distribution of shear stress in bioreactors with EE (open rectangle □) and RM (closed circle ●). Most abundant shear stress appeared around 100 Pa in both bioreactors, and maximum stress was not so different between the two. However, shear stress in rotary bioreactor was generated continuously, as opposed to discontinuous shear stress in reciprocal bioreactor.
Fig. 6. Growth curves and cell viabilities of CHO 1-15 cells.
CHO 1-15 cells were cultivated in bioreactors with EE (open rectangle □) or RM (closed circle ●). (A) Cell viabilities. (B) Growth curves. Batch culture was started at 4 × 104 cells/mL. There was no significant difference in terms of cell growth in either bioreactor; however, cell viability in EE bioreactor suddenly decreased at 200 h.
Fig. 7. tPA activity produced by CHO 1-15 cells.
Production of tPA by CHO 1-15 cells began, along with cell growth, in the bioreactor with EE (open rectangle □) and RM (closed circle ●).